1. Field of the Invention
This invention relates to machines for bending pipes, and more particularly, though not by way of limitation, to machines for automatically hydraulically bending a pipe or tubing to a preselected depth of bend followed by automatic termination of the bending action when the desired bend has been placed in the pipe.
2. Brief Description of the Prior Art
Many types of apparatus for bending cylindrical tubing into shapes suitable for use as tail pipes and mufflers on automobiles, as well as for various other uses, having previously been proposed, and many of these have been patented. In general, such machines employ a hydraulic piston and cylinder assembly to provide the power needed to bend the pipe, and operate on the principle of a die attached to such assembly and advanced against the pipe which is backed up by a pair of grooved shoes which are able to undergo an arcuate swinging movement as the hydraulically impelled die is forced against the pipe at a point where the center of the bend is to be made. As the piston of the piston and cylinder assembly is advanced, the pipe continues to undergo bending, and the shoes continue to swing outwardly. This bending movement is continued until the angle of the pipe which is thus formed has reached the desired magnitude. At this time, the actuation of the hydraulic cylinder is terminated, either by manual manipulation of a valve, or by automatic means which generally includes some type of switch which controls the status of the valve through which hydraulic fluid is passed to the hydraulic cylinder which drives the bending die. The automatic depth of bend control systems previously employed usually include some form of scale or indication device upon which an operator of the apparatus can pre-set a desired depth of bend, indicated in degrees or other indicia. The control mechanism has further included a limit switch system which permits movement of the shoes in their swinging arcuate movement to a certain point, at which point, a limit switch is contacted by a moving element of the assembly, and an electrical circuit is then altered in its status so as to interrupt flow of hydraulic fluid through a valve to the hydraulic cylinder. Further bending is thus automatically terminated at this time.
One of the most widely used types of depth of bend control systems which has been employed to permit an operator to automatically pre-select the degree of bend which he wishes to impart to a pipe has been a system which includes an arcuate protractor-type plate having indicia on the face thereof indicating the degrees which will be included in the angle of bend which the operator selects. A moving pointer is provided in association with this plate which can be moved to a location where the pointer points to, or indicates, the selected depth of bend, in degrees. This swinging pointer or arm generally has a frictional engagement to the plate or another part of the apparatus such that, once set, it will not vibrate from the set position. In some instances, a spring loading feature is incorporated in the depth of bend indicator system to bias the pointer or indicator arm to a selected position and retain it there against possible inadvertent movement. Associated with the indicator arm in such systems is frequently a limit switch which, no matter where the arm is moved, is interposed in the path of movement of some rigid structural element which is coupled or connected to the bending shoes in such a way that this element moves with the shoes during their movement, and in undergoing such movement, contacts the limit switch. At the time of contact with the limit switch, which time is determined by the setting on the indicator plate, an electrical circuit is either opened or closed in a way to cause closure of a valve admitting hydraulic fluid to the hydraulic piston and cylinder assembly used for bending the pipe. Bending is thus automatically terminated at the time that the rigid element coupled to the shoes contacts the limit switch whose position is pre-set by the elected positioning of the indicator arm.
Systems which include a swinging indicator arm and arcuate indicator plate of the type described have presented several disadvantages in usage. One of these disadvantages is that the indicator plate is frequently located in a position which is not readily accessible, and easily visible, to the operator, with the result that the operator must reach over certain parts of the pipe bending apparatus to reach the indicator arm and pre-set it to the selected position on the indicator plate. Moreover, the swinging action of the arm used to select the desired degree of bend, in conjunction with the spring loading of the arm or its frictional setting against displacement when once set, requires some muscualar tension on the part of the operator setting the arm, and consequently, it is sometimes difficult for the operator, on the first attempt, to set the arm pointer at precisely the degree of bend which he wishes to indicate with an arm pointer -- that is, several swings in both directions past the scale reading may occur before he precisely centers the pointer at the right place on the scale.
Another aspect of the systems of the type described which is sometimes a disadvantage is the inability of either the limit switch, or the fixed element which contacts the limit switch, to yield in the event there is a malfunction in the electrical circuitry or the hydraulic system which results in a failure to inactivate the hydraulic system at a time when the limit switch is contacted by the fixed element. This results in either the limit switch being destroyed, or the fixed element being bent or distorted to where it becomes inoperative for future use.
A typical depth of bend control system of the sort previously employed is that which is illustrated and described in Ignoffo, U.S. Pat. No. 3,388,574. The Ignoffo patent includes the described arcuate indicator plate and swingable or movable arm carrying a pointer to indicate a particular degree reading on this plate representing the magnitude of the bend which it is desired to impart to a pipe being bent.
Other patents which show various types of pipe bending machines with swingable arms and arcuate scale plates included therein include Lance, U.S. Pat. No. 3,196,661 and Huth, U.S. Pat. No. 3,429,157. Various other types of systems and structures for controlling and indicating the depth of bend imparted to tubing being bent are described in Traupmann, U.S. Pat. No. 2,867,261; Brinkman, U.S. Pat. No. 2,056,155; Parker et al, U.S. Pat. No. 2,306,223; Chaille, U.S. Pat. No. 2,456,675; Dewitt, U.S. Pat. No. 2,525,403; Bos, U.S. Pat. No. 3,181,321 and Ballar, U.S. Pat. No. 2,357,873.